We have made distinct progress and have secured new funding from the American Cancer Society, and The Whitaker Foundation. In addition the research has formed the basis of 2 Ph.D. and one M.Sc. dissertations. Investigations of tumor oximetry have been extended to human tumors implanted in SCID mice. Distinct changes in regional pO2 have been observed following respiratory challenge and also following targeted thrombosis. In rat tumors we have observed significant changes in tumor oxygenation following irradiation with transient elevation of pO2. (Service 4) REPORT PERIOD: (09/01/97-08/31/98)